1. Field of the Invention
This invention relates to a microcomputer with internal DMA (Direct Memory Access), and in particular to a microcomputer for evaluation, equipped with numerous peripheral resources, and capable of use in common with a plurality of types of microcomputer.
2. Description of the Related Art
A microcomputer has, for example, a CPU, memory such as RAM and ROM, and peripheral resources with various functions, connected via a bus. Peripheral resources have various functions required for control by the microcomputer, such as timer, communication macro, and other functions, and are a type of macro circuit. As memory access control in a microcomputer, in addition to CPU access controlled by the CPU, there is also access controlled by a DMA controller which enables access of memory by peripheral resources, without passing through the CPU. A microcomputer enabling such DMA is for example described in Japanese Patent Laid-open No. 5-53968.
In this Japanese Patent Laid-open Publication No. 5-53968 (laid open Mar. 5, 1993), the automatic assignment of DMA channels to all peripheral device boards, without exception, is described. In this way, in DMA control, unique channel numbers are assigned to all peripheral resources using DMA, and control of DMA access to memory is performed based on these channel numbers. For example, when power is turned on, transfer source addresses and transfer target addresses are registered in the DMA controller for all channels, and in response to DMA requests from peripheral resources the DMA controller references the registered transfer source addresses and transfer target addresses and performs the necessary data transfer control. After the completion of data transfer, the DMA controller transmits a signal to clear the request to the peripheral resource, and causes the peripheral resource issuing the DMA request to withdraw the DMA request. Thus in order to execute DMA control, unique channel numbers must be assigned to peripheral resources requesting DMA access.
In the microcomputer development stage, a microcomputer for evaluation purposes is developed in which a debug support unit is installed, enabling the referencing of data in internal memory from an external device, or the halting and resumption program execution with arbitrary timing. A microcomputer for evaluation is connected to a device to be controlled, the program under development is executed, and the microcomputer for evaluation is used to perform evaluations to determine whether the desired control is being executed, as well as for debugging of the program being developed.
On the other hand, different or identical peripheral resources are often installed on numerous microcomputers possessed by a customer, and the macro data of the numerous peripheral resources developed in the past constitute an important asset for the customer. As explained above, in a microcomputer having DMA functions, unique channel numbers are assigned to the installed peripheral resources. Consequently each peripheral resource has a resource number corresponding to the assigned channel number, and is designed to execute prescribed operations corresponding to this resource number. For example, when some control signal with a resource number is applied by the DMA controller, a peripheral resource references the applied resource number and recognizes that the control signal is addressed to itself, and executes the corresponding control operation. In this way, normally the numerous peripheral resources developed in the past each incorporate a function corresponding to the resource number assigned in the corresponding microcomputer on which the resource is installed.
Hence when arbitrarily combining developed peripheral resources to develop a new microcomputer, if it were possible to install the developed peripheral resource macros in a microcomputer chip for evaluation, debugging tasks and control evaluation in the initial period of the development stage could be begun earlier. However, in actuality resource numbers are assigned corresponding to channel numbers in each developed microcomputer differently. Consequently if the developed peripheral resource macro is installed in the evaluation chip without modification, cases will arise in which the DMA channel numbers do not correspond to the resource numbers of developed peripheral resources. Or, if the developed peripheral resource macro is installed without modification on an evaluation chip, resource numbers of the installed peripheral resources may be repeated, so that correct DMA control becomes impossible.
Due to such circumstances, conventionally when a new microcomputer is being developed, even if a peripheral resource developed in the past is to be used, it has been necessary to develop a new peripheral resource corresponding to a DMA channel of the new microcomputer or to obtain the new peripheral resource by altering the developed peripheral resource, so as to newly develop a microcomputer chip for evaluation incorporating the peripheral resource. This new development of a chip for evaluation increases the cost of development of the microcomputer, and leads to reduced throughput of the development process.